Highly Stretchable and Transparent Ionogels as Nonvolatile Conductors for Dielectric Elastomer Transducers

Abstract

Large deformation of soft materials is harnessed to provide functions in the nascent field of soft machines. This paper describes a new class of systems enabled by highly stretchable, transparent, stable ionogels. We synthesize an ionogel by polymerizing acrylic acid in ionic Using the ionogel and a dielectric elastomer, we fabricate electromechanical transducers that achieve a voltage-induced areal strain of 140%. The ionogel is somewhat hygroscopic, but the transducers remain stable after a million cycles of excitation in a dry oven and in air. The transparency of the ionogels enable the transducers with conductors placed in the path of light, and the nonvolatility of the ionogels enable the transducers to be used in open air.

Ionic skin

“…Whereas familiar elastic gels, such as Jell-O, are brittle and easily rupture, the recent decade has seen the development of hydrogels and ionogels as tough as elastomers. [20][21][22] Many hydrogels are biocompatible. They can be made softer than tissues, achieving the "mechanical invisibility" required for biometric sensors, which monitor soft tissues without 3 constraining them.…”

“…[18][19][20] These gels are polymeric networks swollen with water or ionic liquids. They behave like elastic solids and eliminate the need for containers as required in the case of liquid metal conductors.…”

“…Although most hydrogels dry out in open air, hydrogels containing humectants retain water in environment of low humidity, and ionogels are nonvolatile in vacuum. [18][19][20] We have recently used ionic conductors-together with stretchable and transparent dielectrics-to make actuators, which deform in response to high voltages, on the order of kilovolts. [18] By contrast, the sensors described here deform in response to applied forces, giving signals that can be measured using voltages below 1 volt.…”

3D Printing of Transparent and Conductive Heterogeneous Hydrogel–Elastomer Systems

“…Gel-based ionic circuits thus represent a unique class of devices within stretchable electronics. Conductive gels can be generally divided into those where the ions are provided by solvated salts [25,27] (hydrogels) or by ionic liquids [24,28,29] (ionogels). Although immune to dehydration, ionogels have comparatively lower conductivities than hydrogels.…”

Nanomaterial-based stretchable and transparent electrodes

“…For example, graphene or conducting polymers can be configured into a stretchable form using the pre-strain method, which imparts a wavy structure to the electrode [4,91]. Another strategy is to blend conducting ions with stretchable transparent elastomers or hydrogels [92,93]. These approaches are well described in the previous literature [8][9][10].…”